After some further investigation, we suspect the issue may be occurring on first login for users after the database is successfully created, if there were issues with the current domain being added as an identity provider.
To determine if this is the case, please run the following SQL command:
SELECT * FROM [yourDatabaseNameHere].[dbo].[identity_providers]
If there are no values returned, then your issue is likely what we suspect. To help make sure we address the root cause, please open a support case so that we can gather data like event viewer logs and determine why the identity provider creation failed.
For now, you can try the following workaround to create the "default" identity provider manually:
INSERT INTO [dbo].[identity_providers]
Normally, default IdP name is taken from the DC components of your domain controller (so, mydomain.com is a common format), but in my testing, the name didn't matter.
After running that query to create the db, re-run the select * query and make sure the provider was created, and has Id 1. If it does, at this point, you should be able to log in to your site.